The invention relates to communications, and in particular to a digital radio tuner signal estimator.
Radio architecture has remained remarkably constantxe2x80x94for fifty years radios have been designed around the classic superheterodyne approach. For example, in conventional cellular basestations, each channel has a dedicated receiver tuned exclusively to that specific channel. Each of these receivers requires a fair degree of power, size and expense. This architecture leads to a lot of dedicated receivers in a basestation. Not only are these channels expensive, they are fixed/custom built for a given air interface/modulation standard (e.g., exclusively for AMPS), and tuned for a given channel setting.
However, developments in digital signal processing (DSP) and data conversion are providing radio receiver designers with the tools for more efficient architectures. For example, in the field of wireless base stations, wideband receivers have offered significant benefits, including reductions in base station cost, size, complexity, and power consumption of a basestation. In addition, wideband digital receivers can be rapidly configured to support a variety of air interface/modulation schemes and protocols (e.g., AMPS, NAMPS, TDMA, CDPD, etc.) simultaneously, and switching between them whenever required. Significantly, since the wideband digital receiver processing is performed in software (i.e., in a DSP), the receiver can easily be programmed to support new protocols as they are developed.
In a wideband receiver, the wideband signal is captured, bandshifted to an intermediate frequency (IF) and digitized using the single wide-band radio receiver, which provides a digitized IF signal. The digitized IF signal is then input to a plurality of digital tuners that each mix and filter the digitized IF signal to recover one of the individual channels associated with the tuner. For example, if there are 60 channels each 30 kHz wide, then the receiver must have a bandwidth of at least 3.6 MHz. Advantageously, the wideband receiver is shared between all the channels, instead of having a narrow band receiver dedicated to each channel. Of course, each channel still requires its own circuitry for the final processing, which is generally all digital.
In addition, the flexibility of the digital stage means that the basestation can be quickly xe2x80x9creprogrammedxe2x80x9d to work with new standards. For example, some channels may operate with the conventional analog cellular standard (AMPS), while others use the newer digital IS-54 (TDMA) standard. Notably, because the decoding is performed by software, it can be changed xe2x80x9con the flyxe2x80x9d, so the mix of channels between standards can be changed as required. Indeed, even the channel becomes flexiblexe2x80x94with complete freedom to change from 30 kHz of AMPS or TDMA, to 10 kHz for NAMPS or 1.25 MHz for CDMA. This can be done channel-by-channel as desired.
Since wideband receivers are preferably programmable, each channel digital tuner must accurately lock onto the frequency it is assigned to recover. In addition, estimation of various signal characteristics are often required.
Therefore, there is a need for a computationally efficient technique of signal estimation.
According to the present invention, a digital radio tuner signal estimator receives a digitized in-phase (I) data signal and a digitized quadrature (Q) data signal and provides an estimated amplitude gain signal and an estimated signal-to-noise ratio signal value. The signal estimator includes a symmetrical matched I data digital filter having a first I filter section that filters the received I data signal and provides a first I data signal, and a second I filter section that filters the I data signal and provides a second I data signal. The signal estimator also includes a symmetrical matched Q data digital filter having a first Q filter section that filters the received Q data signal and provides a first Q data signal, and a second Q filter section that filters the Q data signal and provides a second Q data signal. The first and second I data signals and the first and second Q data signals are processed to compute an estimated amplitude gain. In addition, the first and second I data signals and the first and second Q data signals are processed to compute the estimated signal-to-noise ratio value.
The symmetrical matched I data digital filter and the symmetrical matched Q data digital filter preferably comprise poly-phase filters. Other digital filter structures may also be used, including CSD structures.
The signal estimator multiplies the first and second I data signals, and integrates the resultant product to provide a first integrated value. The first and second Q data signals are also multiplied, and the resultant product is integrated to provide a second integrated value. The first and second integrated values are summed to provide a signal indicative of the estimated signal (without noise) noise.
To compute the estimated signal-to-noise ratio signal value, the signal estimator sums the first and second I data signals, computes the square of the resultant sum and provides a first squared signal indicative thereof. The first and second Q data signals are also summed and square of the sum is computed, and a second squared signal indicative thereof is provided. The first and second squared signals are summed and the sum is integrated to provide an integrated summed value, which is processed to provide a signal indicative of estimated signal and noise power. The signals indicative of estimated signal (without noise) power and estimated signal and noise power are processed to compute the estimated signal-to-noise ratio value.
The signal indicative of the estimated signal (without noise) noise is processed to provide the estimated amplitude gain.
The present invention utilizes the symmetry of the FIR matched filter to facilitate providing signal estimation in a digital receiver.
These and other objects, features and advantages of the present invention will become apparent in light of the following detailed description of preferred embodiments thereof, as illustrated in the accompanying drawings.